Postgres 9.5

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Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.

select version();

version

PostgreSQL 9.5.25 on x86_64-pc-linux-musl, compiled by gcc (Alpine 11.2.1_git20220219) 11.2.1 20220219, 64-bit

SELECT 1

CREATE TABLE t (Section CHAR(1), Status VARCHAR(10), Count integer);

INSERT INTO t VALUES ('A', 'Active',   1);
INSERT INTO t VALUES ('A', 'Inactive', 2);
INSERT INTO t VALUES ('B', 'Active',   4);
INSERT INTO t VALUES ('B', 'Inactive', 5);

INSERT 0 1

select * from t

section
status
count

A
Active
1

A
Inactive
2

B
Active
4

B
Inactive
5

SELECT 4

SELECT row_name AS Section,
       category_1::integer AS Active,
       category_2::integer AS Inactive
FROM crosstab('select section::text, status, count::text from t',2)
            AS ct (row_name text, category_1 text, category_2 text);

ERROR:  function crosstab(unknown, integer) does not exist
LINE 4: FROM crosstab('select section::text, status, count::text fro...
             ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.